Recently semiconductor fields require a stable material which may be easily processed and may undergo a burning process at 200° C. or higher because of the high density and high integration of devices. Particularly a polyimide resin has superior heat resistance, chemical resistance, thermal oxidation resistance, etc., and is thus widely utilized not only as an electronic material for use in electrode protecting films and so on of TFT-LCD but also in heat-resistant materials for automobiles, aircrafts, etc.
Initially, a polyimide resin was used in a simple manner by applying a photoresist thereon and then etching it to form a pattern. However, while using a photosensitive polyimide obtained by imparting a photosensitive function to polyimide itself, lithography using a photoresist may be omitted, which contributes to simplifying the process and improving productivity.
Conventional techniques related to positive photosensitive polyimide resins include for example a chemical amplification method for mixing polyamic acid with a photoacid generator which is a photosensitive functional group, a method of mixing polyamic acid with a dissolution inhibitor such as naphtoquinonediazide, a method of mixing soluble polyimide with naphtoquinonediazide, etc. However, such conventional techniques are problematic because the reliability of cured devices may decrease, and it is difficult to obtain a high-resolution pattern, and properties may deteriorate due to the use of a large amount of photosensitive agent.
Also a polyimide resin intrinsically has high aromatic ring density and thus has a yellow color, and undesirably exhibits low transmittance in the visible light range and so has decreased light transmittance.
Typically a polyimide resin is prepared by polymerizing an aromatic diamine and an aromatic dianhydride, thus obtaining a polyamic acid derivative which is then ring-closed and dehydrated at high temperature and imidized. To produce a polyimide resin, the aromatic diamines include oxydianiline (ODA), m-phenylene diamine (m-PDA), bisaminophenyl hexafluoropropane (HFDA), methylenedianiline (MDA), etc., and the aromatic dianhydride includes pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), oxydiphthalic dianhydride (ODPA), etc.
On the other hand, an organic light emitting diode is a display which is configured such that a thin film is formed between two electrodes using an organic light emitting material, and current is applied to both electrodes, whereby electrons and holes which are carriers are injected into an organic thin film layer at the anode and cathode so that these carriers are recombined to generate energy which is then emitted in the form of light. This uses properties in which an organic material emits light when voltage is applied thereto, and color tones are represented using properties according to which red, green and blue colors are given off depending on the kind of organic material.
The OLED is manufactured by for example coating a transparent substrate having indium thin oxide (ITO) or the like as a transparent electrode deposited thereon with a photoresist, performing photoexposure, developing, etching and stripping, thus forming a pattern, forming an insulating layer thereon using a photoresist, and then forming a barrier on the insulating layer pattern. Then, an organic thin film is deposited in the order of an electron injection layer, an electron transport layer, a light emitting layer, a hole transport layer and a hole injection layer, after which a metal electrode layer is deposited thereon. Finally, sealing is performed using a sealant and a module is then assembled, thereby completing an OLED.
The insulating layer patterning process as described above is performed by uniformly applying a liquid positive-type photosensitive resin composition over the entire surface of a substrate using spin coating, and then conducting prebaking and photo exposure to form a circuit. To prevent deterioration of ITO edges and upper and lower shorts, an insulating layer having a thickness of 1000˜1200 Å is formed.
The insulating layer includes an inorganic insulating film or an organic insulating film. The inorganic insulating film material may include one or more selected from among SiO2, SiNx and so on.
Not only the inorganic insulating film but also the organic insulating film such as an imide based polymer or an acrylic polymer may be formed using an insulative photosensitive resin composition, but it is not easy to ensure a process margin due to partial residue generation or the like in the process and it is difficult to apply to a highly sensitive pattern. Also, the conventional polyimide resulting from a diamine and a dianhydride intrinsically has a brown color, and is thus can only improve the light transmittance to a limited extent.
Hence, there is a need for a photosensitive resin composition which is capable of forming a highly sensitive circuit without residue generation in a developing process, improving the color of conventional polyimide to increase light transmittance, and ensuring insulation resistance.